1. Field of the Invention
The present invention relates to an AC voltage regulator to be placed between an AC voltage power source, such as a utility line, and its load, so as to regulate the voltage supplied to the load independent of the variations of the line voltage above or below a desired output, within a predetermined range, and to be substantially compact, efficient and economical to use.
2. Description of the Related Art
AC power voltage sources are frequently subjected to variations from their desired output voltage due to numerous common factors. For example, the demand of multiple loads, the impedance of the transmission lines, changes in average power demands over time, along with various other factors can cause the voltage output from the source to fluctuate, both above and below the desired output, before reaching the load. As a result, these variations can seriously affect the electrical devices connected thereto. In particular, many delicate industrial machines or electronic equipment, which are difficult and expensive to repair and/or replace, are highly susceptible to the adverse effects of voltage fluctuations. Accordingly, voltage regulators are often utilized in an attempt to stabilize the voltage output and bring it closer to the desired voltage output for the particular load.
Most prior art tap-changer AC voltage regulators utilize a small number of discrete steps in a tapped auto-transformer to correct changes in the voltage level of the AC power source. These corrections, however, are merely coarse corrections because discrete steps must be taken. Further, because of size constraints of the regulator, only a few discrete steps are available, thereby limiting a variation of the output to a small range of values and/or allowing significant variation between steps. Additionally, because the taps are switched at the power section of the windings, the power dissipation in the switching devices will greatly impair the efficiency of the regulator and limit the power that it can handle.
Accordingly, others in the art have turned to using switches at secondary windings, in what had been referred to as "phasorial" or "vectorial" AC voltage regulators. In these devices each of the switches handles five or six times less power than the tap-changer regulator for the same output power level. Nevertheless, while the taps are switched at the low power section, a large amount of secondary winding is needed to fulfill the full range necessary. This requirement makes these types of regulators very bulky and limits the number of possible steps. Additionally, voltage levels induced in the secondary winding puts considerable stress on the switching devices which therefore limits the line voltage levels for which the device can be practically used. Accordingly, there is still a need for a voltage regulator which is substantially compact and can handle a broad range of voltage variations efficiently and cost effectively.
More recently, AC switching regulators, as recited in the patents to McGuire (U.S. Pat. No. 4,745,352 and 4,791,348) which uses a single tap auto-transformer, have been implemented. These regulators, which switch at high frequency in PWM mode part of their winding between two predetermined points, and filter the output, can obtain a controllable average voltage at that output. In such systems, however, the AC voltage must either be boosted (step-up), thus correcting AC power variations below the specified required output values, or be stepped-down, thus correcting variations above the specified desired voltage output. Accordingly, a user is forced to select which side of the variation is most likely to occur and must implement the corresponding device, a decision that can be quite costly if improperly made. Further complicating the decision, in many circumstances the voltage can fluctuate both above and below the specified desired output. Therefore, to ensure safety in such circumstances, there are two alternatives, either to utilize two regulators, one in a stepping-up mode and another in a stepping-down mode, a configuration which may not be practical, doubles the costs, requiring two full power transformers, and can be quite bulky, or use a stepping-up transformer and a stepping-down regulator, both with twice the range, also an alternative that impractical and can even be dangerous for the user.
As a result, there is still a substantial need in the art for a voltage regulator which will accurately and effectively regulate the voltage output to a specified desired voltage output, is not substantially bulky or substantially expensive, and is capable of providing the necessary adjustments for voltage levels above or below the desired output utilizing only a single transformer.